Communication devices such as User Equipments (UE) are enabled to communicate wirelessly in a wireless communications network, sometimes also referred to as a wireless communication system, a cellular radio system or a cellular system. The communication may be performed e.g. between two user equipments, between a user equipment and a regular telephone and/or between a user equipment and a server via a Radio Access Network (RAN) and possibly one or more core networks, comprised within the wireless communications network.
User equipments are also known as e.g. mobile terminals, wireless terminals and/or mobile stations, mobile telephones, cellular telephones, or laptops with wireless capability, just to mention some examples. The user equipments in the present context may be, for example, portable, pocket-storable, hand-held, computer-comprised, or vehicle-mounted mobile devices, enabled to communicate voice and/or data, via the RAN, with another entity.
The wireless communications network covers a geographical area which is divided into cell areas, wherein each cell area being served by a network node such as a Base Station (BS), e.g. a Radio Base Station (RBS), which sometimes may be referred to as e.g. eNB, eNodeB, NodeB, B node, or BTS (Base Transceiver Station), depending on the technology and terminology used. The base stations may be of different classes such as e.g. macro eNodeB, home eNodeB or pico base station, based on transmission power and thereby also cell size. A cell is the geographical area where radio coverage is provided by the base station at a base station site. One base station, situated on the base station site, may serve one or several cells. Further, each base station may support one or several radio access and communication technologies. The base stations communicate over the radio interface operating on radio frequencies with the user equipments within range of the base stations.
In some RANs, several base stations may be connected, e.g. by landlines or microwave, to a radio network controller, e.g. a Radio Network Controller (RNC) in Universal Mobile Telecommunications System (UMTS), and/or to each other. The radio network controller, also sometimes termed a Base Station Controller (BSC) e.g. in GSM, may supervise and coordinate various activities of the plural base stations connected thereto. GSM is an abbreviation for Global System for Mobile Communications (originally: Groupe Spécial Mobile).
In the context of this disclosure, the expression Downlink (DL) is used for the transmission path from the base station to the mobile station. The expression Uplink (UL) is used for the transmission path in the opposite direction i.e. from the mobile station to the base station.
In 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE), base stations, which may be referred to as eNodeBs or even eNBs, may be directly connected to one or more core networks.
UMTS is a third generation mobile communication system, which evolved from the GSM, and is intended to provide improved mobile communication services based on Wideband Code Division Multiple Access (WCDMA) access technology. UMTS Terrestrial Radio Access Network (UTRAN) is essentially a radio access network using wideband code division multiple access for user equipments. The 3GPP has undertaken to evolve further the UTRAN and GSM based radio access network technologies.
According to 3GPP/GERAN, a user equipment has a multi-slot class, which determines the maximum transfer rate in the uplink and downlink direction. GERAN is an abbreviation for GSM EDGE Radio Access Network. EDGE is further an abbreviation for Enhanced Data rates for GSM Evolution.
When a user equipment is powered on, it starts an initial cell selection procedure. The purpose of the initial cell selection procedure is to ensure that the user equipment gets into service as fast as possible. The user equipment uses this procedure to scan all Radio Frequency (RF) channels in the E-UTRA bands according to its capabilities to find a suitable cell, where suitable refers to a combination of radio measurements based criteria, e.g. a Reference Signal Received Power (RSRP) and other criteria, e.g. the cell belonging to a Public Land Mobile Network (PLMN) that the user equipment is allowed to camp on.
Once the user equipment camps on a suitable cell, it continues to search for the best cell to camp on. This procedure is called cell reselection. Its purpose is to ensure that the user equipment always camps on the cell that is best in terms of some predetermined set of criteria called the cell ranking criteria. Broadly speaking, cell reselection is the basic idle mode mobility procedure that ensures that the user equipment continuously may receive system broadcast information and continuously may be paged within the coverage area of its PLMN. Cell reselection also ensures that once paged, the user equipment will enter connected mode in a cell that provides good coverage.
Handover refers to the transfer of an ongoing call or data session from one channel connected to a core network to another channel.
Cell change may be used to describe the mobility when the user equipment performs inter-radio access technology (inter-RAT) handovers, e.g. between a GERAN and a WCDMA network. In some networks, such an inter-RAT cell change is supported by sending system information of the new network while still connected to the old network and thereby facilitating the inter-RAT mobility procedure. Cell change may also refer to the collection of idle and connected mode mobility, such as cell (re-)selection and handover procedures, but it may also include the cases of inter-RAT and inter-frequency mobility.
In network assisted Device-to-Device (D2D) communications underlaying a cellular infrastructure, user equipments in the proximity of each other may establish a direct radio link, also referred to as a device-to-device link or bearer. In this description, the expression device-to-device will be referred to as D2D. Network assisted D2D communications is sometimes also referred to as network D2D communications underlaying a cellular radio access network, or for short D2D as a RAN underlay.
While the user equipments communicate over the D2D link, they also maintain a cellular connection with their respective serving network node, i.e. serving base station. That way the cellular RAN may assist and supervise the user equipments in allocating cellular resources for the D2D link, comprising e.g. mode selection, indicating a maximum power level to the transmitting user equipment and, in general protecting the D2D link from interference from cellular user equipments or base stations. Likewise, the cellular RAN has means to protect the cellular communications links, herein also sometimes referred to as cellular bearers, from harmful interference caused by transmitting D2D user equipments.
FIG. 1 schematically illustrates a network assisted D2D communications scenario in a RAN according to prior art. A user equipment A, UE-A, capable of D2D communication is connected to a first network node, e.g. a serving base station eNB-A, and a user equipment B, UE-B, capable of D2D communication is connected to a second network node, e.g. a serving base station eNB-B. The RAN comprises in this example the user equipments UE-A, UE-B; the first and second network nodes, eNB-A, eNB-B, and cellular user equipments UE-1 and UE-2 having a cellular connection, e.g. a cellular link, with their respective serving network node, eNB-A and eNB-B. Further, the user equipment A and the user equipment B are in the proximity of each other. In such a case, the RAN may assist the user equipments A, and B to establish a D2D link over which the user equipments A, and B communicate.
When used in this description, by user equipments in the proximity of each other is meant user equipments that are positioning within a distance of 100-150 m from each other. However, devices communicating in licensed spectrum bands, and consequently allowed to transmit with higher power levels, such as 24 dBm, may, under certain propagation conditions, be able to discover and transfer data to each other over larger distances, e.g. over distances up to 1000 m.
While the user equipments A, and B communicate over the D2D link, they also maintain a cellular connection with their respective serving base station eNB-A, eNB-B, cf. FIG. 1. In this way the cellular RAN assists the user equipments A, and B in allocating cellular resources for the D2D link, indicating a maximum power level to the transmitting user equipment and, in general protecting the D2D link from interference from cellular user equipments or base stations. The basic rationale for network assisted D2D communications is to allow short range direct communication between user equipments utilizing cellular spectrum.
FIG. 2 schematically illustrates a part of a communications network comprising user equipments 202 with D2D communication functionality, user equipments 204 without D2D communication functionality, and a radio network node 206. The radio network node 206 provides radio coverage over at least one geographic area forming a cell 208.
The user equipments 202 with D2D communication capability is herein sometimes referred to as a D2D capable user equipments 202, and the user equipments 204 without D2D communication functionality is herein sometimes referred to as a cellular user equipments 204 and/or a legacy user equipments 204.
Further, FIG. 2 schematically illustrates a typical coexistence scenario between cellular user equipments 204 and user equipments 202 having D2D functionality. As schematically illustrated, the user equipments 202-1 constitute a first D2D pair; D2D pair 1, the user equipments 202-2 constitute a second D2D pair; D2D pair 2, and the user equipments 202-3 constitute a third D2D pair; D2D pair 3.
In this scenario it is assumed that the D2D link between the user equipments 202 of a D2D pair uses uplink spectrum resources. In such case the receiver (not shown) of one of the user equipments 202 in a D2D pair may suffer from interference from transmission from the cellular user equipments 204, while the network node 206 may suffer from interference from transmission from a transmitter (not shown) of one of the user equipments 202 in a D2D pair.
D2D communication capable user equipments are expected to be introduced gradually into existing and evolving cellular networks, such as the 3GPP LTE and LTE-Advanced networks.
The resources used for the D2D communication link between user equipments 202 of a D2D pair may partly overlap with the resources used by the cellular, legacy, user equipments 204 for communication with their respective serving network node 206.
As schematically illustrated in FIG. 2, when the D2D links of the D2D pairs are allocated uplink resources, three types of interference situations may arise.
Type-1 interference is caused by transmitting cellular user equipments 204 transmitting in UL resources causing interference to receiving user equipment 202 capable of D2D communication.
Type-2 interference is caused by user equipments 202 capable of D2D communication and transmitting in UL resources causing interference to the receiving D2D capable user equipments 202 of other D2D pairs.
Type-3 interference is caused by user equipments 202 capable of D2D communication and transmitting in UL resources causing interference to the radio network node 206.
In existing cellular systems, the cellular user equipments are required to make physical layer measurements of the downlink radio characteristics. Such measurements are typically reported to the higher layers and are used for a variety of purposes, notably for various types of handover decisions made in the RAN. They are also used for other mobility functions such as change of Primary Cell (PCell) or Primary Component Carrier (PCC) in multi-carrier systems, also known as a carrier aggregation. The measurements are also used autonomously by the cellular user equipment for performing cell selection, i.e. initial cell selection, cell reselection, in idle or low activity states.
The physical layer measurements performed by the cellular user equipments are typically of type: signal strength measurements, e.g. measurements of Reference Signal Receive Power (RSRP) in LTE, or signal quality measurements e.g. measurements of Reference Signal Received Quality (RSRQ) in LTE. The measurements of RSRP and RSRQ may be absolute as well as relative measurement quantities.
For the absolute measurement, the RSRP and RSRQ are measured from one cell, e.g. from a serving cell or a neighbour cell. The user equipment may report the absolute measurement results periodically. However, the absolute measurement from the serving cell or the neighbour cell may also be compared with a threshold value by the user equipment. The threshold value may be configured by the network but it may also be pre-defined. The results of the comparison may be reported by the user equipment in terms of an event, e.g. the user equipment may report an event if neighbour cell RSRQ is above a threshold value of X dB, wherein X may be a value between 2 and 6 dB.
The event may be a form of a measurement report which is sent by the user equipment to the network when certain conditions are met. For example, as previously described the user equipment reports an event if a neighbour cell RSRQ is above a threshold value of X dB, e.g. 2 dB.
The relative measurement may be obtained by comparing the measurements done on the serving cell and neighbour cells with each other. The results of the comparison of the serving cell and the neighbour cell measurement results may also be reported by the user equipment in terms of an event, e.g. the user equipment may report an event if neighbour cell RSRQ compared to serving cell RSRQ is above a threshold value of Y dB, wherein Y may be a value between 2 and 4 dB.
As illustrated in FIG. 2, in order for the radio network node 206 to be able to schedule resources, e.g. Physical Resource Blocks (FRB), for D2D communication and to set the maximum transmission power of the transmitting user equipment 202 capable of D2D communication, the radio network node 206 requires to have knowledge or at least an estimation about the Interference caused by cellular user equipments 204 at the receiving user equipment 202 capable of D2D communication and to have knowledge or at least an estimation about path loss between the cellular user equipment 204 and the receiving user equipments 202 capable of D2D communication.
A drawback with the prior art system is the lack of information about either the interference caused at the receiving user equipment 202 capable of D2D communication or the path loss between cellular user equipments 204 and receiving user equipment 202 capable of D2D communication.